Position-sensitive transition-edge sensor (TES) microcalorimeters (PoSTs) were developed to detect gamma rays up to a few MeV. Each gamma-ray PoST comprised a 0.5 mm × 0.5 mm × 19 mm lead absorber with a TES on each end and worked as a 1D imaging spectrometer. Only one TES worked at low temperature and its results are reported herein. We irradiated the PoST device with gamma rays from a Cs-137 source, and the resultant pulses showed strong correlations between the pulse height and the rise time. To determine effective pixels, we separately divided the photopeak and lead-K escape peak pulses into 19 groups after sorting them by their rise times. From the pulse shape distributions, we concluded that the TES was sensitive to the gamma-ray interaction position as long as it was not located too far away from the TES, and that it was probably possible to determine the interaction positions of the entire absorber, if both TESs were working. The PoST device was then modeled and the average pulses of the 19 effective pixels were compared to those of numerical simulations, where the rise time distributions of the actual pulses and simulated pulses were in good agreement.
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